The Importance of pH and Liming

Soil pH influences many of the chemical and biological properties of soils that are important to the growth of plants.  Acid pH levels commonly decrease availability of nutrients like nitrogen and phosphorous to the point where plant growth can be significantly reduced.  A common technique to alleviate problems associated with acidity is by adding liming materials. Often times we solely focus on fertilizer application and neglect considering the importance pH plays in nutrient availability. The following picture illustrates the availability of nutrients to plants at different pH values. Notice the most relative availability, according to the graph, occurs at pH of 6.5 as opposed to the lesser availability at pH of 4.5 and 9.


When liming a soil, the amount applied is dependent upon several factors.  In general, sandy soils need less lime to get a desired pH change compared to fine textured soils.  This is due to sandy soils having a lower CEC (cation exchange capacity) compared to fine textured soils. CEC values are usually listed on your soil test report.  With a lower CEC, the soil will generally require less lime.  The amount of lime applied is also dependent upon the magnitude of the change in pH required.  A small change in pH requires less lime compared to a large change. The chemical composition of the liming material along with the fineness of the liming material will also determine the amount needed. The fall is a good time of year for lime applications, since lime should be applied 3 to 6 months before planting.

Ground limestone is the most common and most widely used of all liming materials. It is relatively cheap compared to the other types of lime. The two important minerals found in ground limestones are calcite and dolomite. When little or no dolomite is present it is referred to as calcitic limestone; as the magnesium content increases, it grades into dolomitic limestone.

The effectiveness of a liming material is determined by its chemical makeup. 100% pure limestone is considered to be 100% effective in its ability to neutralize acidity. Hard limestones need to be ground to sizes specified by law to increase their solubility through increasing surface area.

The following requirements are specified by Mississippi law:


Item                                                                                             Efficiency rating

Material passing a 60-mesh sieve                                                        100%

Material passing a 10-mesh sieve but not a 60-mesh sieve                 50%

Material not passing a 10-mesh sieve                                                  0%


Example:  The relative efficiency rating of calcitic limestone consisting of 80% passing a 60-mesh sieve, 17% passing a 10-mesh but not a 60-mesh sieve, and 3% not passing a 10-mesh sieve.

60-mesh                                   .80 x 100% =   80%

10-mesh                                   .17 x 50% =       8.5%

>10-mesh                            __.03 x 0% =         0%____

Sum =              88.5%

Given this lime has a CaCO3 equivalent of 93%, its effectiveness would be 0.93 x 88.5% = 82.3%.  Thus if the lime recommendations were 1 ton of 100% CaCO3 lime per acre, it would require 2000/.82 = 2439 pounds of this particular lime.


Site Location for a Vegetable Garden

The first step in having a successful vegetable garden is proper site selection. Three main things to consider when deciding where to locate your vegetable garden is whether or not plants will have access to sunlight, fertile soil and water. Most vegetables need at least six hours of full or direct sunlight per day for optimum growth. Obviously, you want to avoid areas such as next to large trees and buildings that could block needed sunlight from plants causing future issues.

Another requirement for producing an abundance of fresh vegetables is good soil. If the soil is hard, rocky, soggy, or nutrient-poor, the vegetables will be, too. In general, vegetable garden soil should be well draining and loose with plenty of organic matter. Poorly drained, fine textured soils such as clay or soils that are too coarse like sand are not ideal. A soil with a high clay content will drain slowly, having the potential to cut off the oxygen supply to plants roots. On the other hand, if the soil is too sandy it may drain too quickly before plants are able to take up the proper amount of much needed water.

If you have a large coffee can you can check the drainage of your new garden site by demonstrating a percolation test.

Percolation Test Photo: C.Robertson Swarthmore College
Percolation Test
Photo: C.Robertson
Swarthmore College

Dig a 4 inch hole that is wide enough for the can and cutting out the bottom of the can. Firmly place the can in the hole so that nothing can escape around the outside edges of the bottom. Fill the can up and watch the water level for an hour. If less than 2 inches drains you have a poorly draining location and 5 or more inches drains then your soil drains a bit too quick. If you don’t have a coffee can you can still dig the hole and fill it with water just bear in mind that some of the water will travel laterally in the soil.

Even though a heavy clay soil like most of our soils here in the delta may be less than ideal for growing vegetables, practicing proper management strategies can help make these soils more optimum. Increasing the organic matter content of a clay soil makes it easier to work, and improves the internal drainage. Increasing the soil’s organic matter content can be done by adding manure, composted leaves, sawdust, bark, etc. Since pH and fertilizer needs vary by type of vegetable, it is important to have your soil tested to help you make the proper adjustments.

Last but definitely not least, your vegetable garden should be located close to a water source. Whether it be in row crop situation, home horticulture or vegetable gardening, water usually the most limiting factor effecting yield.  Vegetable gardens usually use about 1 – 2 inches of water per week during the growing season. Locating your garden near a water source gives you few excuses for letting the garden stress during the heat of summer or in dry weather conditions. Adequate soil moisture is important for seed germination, uniform growth, and productivity. Easy access to a garden hose means less lugging-around of watering cans, and it also helps if you decide to install soaker hoses or a drip irrigation system.

Onions irrigated by drip irrigation. Photo (Michigan State University Extension)
Onions irrigated by drip irrigation.
Photo (Michigan State University Extension)

Other factors to consider is how much produce will be needed to fulfill the needs of family and friends. Places that have been overlooked could have potential weed problems in the future. Try to steer clear from locations with morningglory, nutsedge, and bermudagrass. Also don’t forget to flag off or fence in a site to keep pets and children from playing in the garden. If there is a wildlife that frequents the area, the use of an electric fence could be the best option. Don’t hesitate to contact your local county extension office and ask questions or advice.

Soil Testing in Preparation for the Growing Season

There are many factors that affect crop growth and yield production. Some of these factors cannot be controlled, such as, climate. However, factors such as soil fertility can be controlled and managed to maximize productivity. An effective way to help control soil fertility is through soil testing. Crops require large amounts of plant nutrients that must be supplied in proper balance from the soil. Managing nutrients helps to optimize productivity and profitability of crops while maximizing efficiency of nutrient use, all while keeping environmental impact at a minimum. Soil tests measure plant available nutrients and provide and index of nutrient availability in the soil. This serves as an excellent guide to profitable use of commercial liming and fertilizer. Justus von Liebig’s Law of the Minimum states that yield is proportional to the amount of the most limiting nutrient:

Every field contains a maximum of one or more and a minimum of one or more nutrients. With this minimum, be it lime, potash, phosphoric acid, magnesia, or any other nutrient, the yields stand in direct relation. It is the factor that governs and controls…yields…

In other words, crops will only produce as much as its most limiting factor allows. Routine soil testing is an outstanding tool to help identify controllable limiting factors when it comes to nutrient availability.

As humans, we are dependent upon agriculture for food, fiber, and shelter. All of which are necessary to our survival. The responsibility of producing these essentials falls on the shoulders of our farmers. However, as we depend on them for our basic needs, farmers depend on the soil for their production. Soil fertility and nutrient management are essential to the continued production of food, fiber and shelter for an ever growing world population. Proper soil fertility and nutrient management starts will soil testing.  Agricultural fields should be tested every 3 years or once per crop rotation. For spring planting, soil samples should be collected between mid-October to January. For more information, such as, good sampling technique and interpreting soil test reports visit your local county Extension Office.

2016 Delta Ag Expo

It’s that time of year again. The 43rd Annual Delta Ag Expo will be held in Cleveland, MS at the Bolivar County Exposition Center on Wednesday, January 20 from 8:30 am to 4 pm and on Thursday, January 21 from 8:30 am to 12 pm.

Expo Logo

Beginning in 1974, the Delta Ag Expo is an annual event that is cosponsored by the Delta Agricultural Exposition Corporation and the Mississippi State University Extension Service and is held at the Bolivar County Expo Center in Cleveland, MS. This is an educational event that presents the latest technical information relating to agricultural crops grown in the Delta and surrounding area. This is accomplished annually by providing educational seminars highlighting the newest technology and research-proven agricultural information as well as providing over 100 commercial exhibits representing every phase of agriculture. This event provides the farmer an opportunity to talk with Extension and research personnel, commercial ag-related businesses, and see the latest changes in technology first-hand all under one roof.


The 2016 Expo is headlined by Dr. Darren Hudson, Director for the International Center for Agriculture Competitiveness to be the keynote speaker. Dr. Hudson will be addressing Trends in Competitiveness of U.S. and Global Agriculture and Impacts on MS Delta Agriculture.

For more information please visit